This disclosure relates to techniques for investigating subsurface formations and reservoirs. In particular, this disclosure relates to techniques for subsurface investigations involving, for example, basin and petroleum system modeling and Curie depth analysis.
While the demand for petroleum is ever increasing, the cost of exploration to find new reserves is increasing as well. The risk of drilling dry holes and lost investment can be significant. One way to reduce investment risk in oil and gas exploration is to ascertain the presence, types and volumes of hydrocarbons in a prospective structure before drilling. Investigative techniques, such as seismic surveying and interpretation, can be used to delineate closed subsurface structures and identify potential subsurface traps for hydrocarbons, provided such techniques reliably predict the content in the traps. Closed structures, even those located near producing oil fields, may not contain commercially producible amounts of oil or gas.
To obtain knowledge of the type and the volume of hydrocarbons in a prospective subsurface formation before drilling, geologic elements and models can be combined and processed. Investigative techniques, such as basin and petroleum system modeling (basin modeling), may be used to analyze subsurface formations. Basin modeling may allow geoscientists to model aspects of the subsurface formation, such as dynamics of sedimentary basins and their associated fluids. Basin modeling may be used, for example, to generate basin models for determining if past conditions were suitable for hydrocarbons to fill potential reservoirs and be preserved therein.
With basin modeling, the evolution of a basin may be tracked through time as the basin fills with fluids and sediments that may eventually generate or contain hydrocarbons. See for example, Mubarak M. Al-Hajeri et al., “Basin and Petroleum System Modeling”, Oilfield Review, Summer 2009, 21, No. 2, pages 14-29, or Thomas Hantschel et al., “Fundamentals of Basin and Petroleum Systems Modeling”, Springer-Verlag, 2009. Basin modeling may involve simulating processes, such as sediment deposition, faulting, burial, kerogen maturation kinetics and multiphase fluid flow. Basin modeling can combine data from geology, geophysics, geochemistry, hydrodynamics and thermodynamics.
In concept, basin modeling may be analogous to a reservoir simulation. Reservoir simulators may model fluid flow during petroleum drainage to predict and optimize production, with a distance scale on the order of meters to kilometers and a time scale on the order of months to years. Basin modeling may be used to simulate hydrocarbon-generation processes (e.g., to calculate charge or volume of hydrocarbons available for entrapment, as well as the fluid flow to predict the volumes and locations of accumulations and their properties), with a distance scale on the order of tens to hundreds of kilometers and a time scale on the order of millions of years. In basin modeling, model geometry can be dynamic and change during simulation.
Another investigative technique used to analyze subsurface formations involves a determination of Curie depth. Curie depth is the depth below the earth's surface at which rocks in a specific geographical area encounter the Curie temperature. Curie depth is also the depth at which subsurface materials change from ferromagnetic to paramagnetic, a change which is detectable using magnetic measurements. This depth can be approximated, for example, from aeromagnetic survey data, spectral analysis, or forward modeling.